Doc/library/asyncio-protocol.rst
.. currentmodule:: asyncio
.. _asyncio-transports-protocols:
.. rubric:: Preface
Transports and Protocols are used by the low-level event loop
APIs such as :meth:loop.create_connection. They use
callback-based programming style and enable high-performance
implementations of network or IPC protocols (e.g. HTTP).
Essentially, transports and protocols should only be used in libraries and frameworks and never in high-level asyncio applications.
This documentation page covers both Transports_ and Protocols_.
.. rubric:: Introduction
At the highest level, the transport is concerned with how bytes are transmitted, while the protocol determines which bytes to transmit (and to some extent when).
A different way of saying the same thing: a transport is an abstraction for a socket (or similar I/O endpoint) while a protocol is an abstraction for an application, from the transport's point of view.
Yet another view is the transport and protocol interfaces together define an abstract interface for using network I/O and interprocess I/O.
There is always a 1:1 relationship between transport and protocol objects: the protocol calls transport methods to send data, while the transport calls protocol methods to pass it data that has been received.
Most of connection oriented event loop methods
(such as :meth:loop.create_connection) usually accept a
protocol_factory argument used to create a Protocol object
for an accepted connection, represented by a Transport object.
Such methods usually return a tuple of (transport, protocol).
.. rubric:: Contents
This documentation page contains the following sections:
The Transports_ section documents asyncio :class:BaseTransport,
:class:ReadTransport, :class:WriteTransport, :class:Transport,
:class:DatagramTransport, and :class:SubprocessTransport
classes.
The Protocols_ section documents asyncio :class:BaseProtocol,
:class:Protocol, :class:BufferedProtocol,
:class:DatagramProtocol, and :class:SubprocessProtocol classes.
The Examples_ section showcases how to work with transports,
protocols, and low-level event loop APIs.
.. _asyncio-transport:
Source code: :source:Lib/asyncio/transports.py
Transports are classes provided by :mod:asyncio in order to abstract
various kinds of communication channels.
Transport objects are always instantiated by an
:ref:asyncio event loop <asyncio-event-loop>.
asyncio implements transports for TCP, UDP, SSL, and subprocess pipes. The methods available on a transport depend on the transport's kind.
The transport classes are :ref:not thread safe <asyncio-multithreading>.
.. class:: BaseTransport
Base class for all transports. Contains methods that all asyncio transports share.
.. class:: WriteTransport(BaseTransport)
A base transport for write-only connections.
Instances of the WriteTransport class are returned from
the :meth:loop.connect_write_pipe event loop method and
are also used by subprocess-related methods like
:meth:loop.subprocess_exec.
.. class:: ReadTransport(BaseTransport)
A base transport for read-only connections.
Instances of the ReadTransport class are returned from
the :meth:loop.connect_read_pipe event loop method and
are also used by subprocess-related methods like
:meth:loop.subprocess_exec.
.. class:: Transport(WriteTransport, ReadTransport)
Interface representing a bidirectional transport, such as a TCP connection.
The user does not instantiate a transport directly; they call a utility function, passing it a protocol factory and other information necessary to create the transport and protocol.
Instances of the Transport class are returned from or used by
event loop methods like :meth:loop.create_connection,
:meth:loop.create_unix_connection,
:meth:loop.create_server, :meth:loop.sendfile, etc.
.. class:: DatagramTransport(BaseTransport)
A transport for datagram (UDP) connections.
Instances of the DatagramTransport class are returned from
the :meth:loop.create_datagram_endpoint event loop method.
.. class:: SubprocessTransport(BaseTransport)
An abstraction to represent a connection between a parent and its child OS process.
Instances of the SubprocessTransport class are returned from
event loop methods :meth:loop.subprocess_shell and
:meth:loop.subprocess_exec.
.. method:: BaseTransport.close()
Close the transport.
If the transport has a buffer for outgoing
data, buffered data will be flushed asynchronously. No more data
will be received. After all buffered data is flushed, the
protocol's :meth:protocol.connection_lost() <BaseProtocol.connection_lost> method will be called with
:const:None as its argument. The transport should not be
used once it is closed.
.. method:: BaseTransport.is_closing()
Return True if the transport is closing or is closed.
.. method:: BaseTransport.get_extra_info(name, default=None)
Return information about the transport or underlying resources it uses.
name is a string representing the piece of transport-specific information to get.
default is the value to return if the information is not available, or if the transport does not support querying it with the given third-party event loop implementation or on the current platform.
For example, the following code attempts to get the underlying socket object of the transport::
sock = transport.get_extra_info('socket')
if sock is not None:
print(sock.getsockopt(...))
Categories of information that can be queried on some transports:
socket:
'peername': the remote address to which the socket is
connected, result of :meth:socket.socket.getpeername
(None on error)
'socket': :class:socket.socket instance
'sockname': the socket's own address,
result of :meth:socket.socket.getsockname
SSL socket:
'compression': the compression algorithm being used as a
string, or None if the connection isn't compressed; result
of :meth:ssl.SSLSocket.compression
'cipher': a three-value tuple containing the name of the
cipher being used, the version of the SSL protocol that defines
its use, and the number of secret bits being used; result of
:meth:ssl.SSLSocket.cipher
'peercert': peer certificate; result of
:meth:ssl.SSLSocket.getpeercert
'sslcontext': :class:ssl.SSLContext instance
'ssl_object': :class:ssl.SSLObject or
:class:ssl.SSLSocket instance
pipe:
'pipe': pipe objectsubprocess:
'subprocess': :class:subprocess.Popen instance.. method:: BaseTransport.set_protocol(protocol)
Set a new protocol.
Switching protocol should only be done when both protocols are documented to support the switch.
.. method:: BaseTransport.get_protocol()
Return the current protocol.
.. method:: ReadTransport.is_reading()
Return True if the transport is receiving new data.
.. versionadded:: 3.7
.. method:: ReadTransport.pause_reading()
Pause the receiving end of the transport. No data will be passed to
the protocol's :meth:protocol.data_received() <Protocol.data_received>
method until :meth:resume_reading is called.
.. versionchanged:: 3.7 The method is idempotent, i.e. it can be called when the transport is already paused or closed.
.. method:: ReadTransport.resume_reading()
Resume the receiving end. The protocol's
:meth:protocol.data_received() <Protocol.data_received> method
will be called once again if some data is available for reading.
.. versionchanged:: 3.7 The method is idempotent, i.e. it can be called when the transport is already reading.
.. method:: WriteTransport.abort()
Close the transport immediately, without waiting for pending operations
to complete. Buffered data will be lost. No more data will be received.
The protocol's :meth:protocol.connection_lost() <BaseProtocol.connection_lost> method will eventually be
called with :const:None as its argument.
.. method:: WriteTransport.can_write_eof()
Return :const:True if the transport supports
:meth:~WriteTransport.write_eof, :const:False if not.
.. method:: WriteTransport.get_write_buffer_size()
Return the current size of the output buffer used by the transport.
.. method:: WriteTransport.get_write_buffer_limits()
Get the high and low watermarks for write flow control. Return a
tuple (low, high) where low and high are positive number of
bytes.
Use :meth:set_write_buffer_limits to set the limits.
.. versionadded:: 3.4.2
.. method:: WriteTransport.set_write_buffer_limits(high=None, low=None)
Set the high and low watermarks for write flow control.
These two values (measured in number of
bytes) control when the protocol's
:meth:protocol.pause_writing() <BaseProtocol.pause_writing>
and :meth:protocol.resume_writing() <BaseProtocol.resume_writing>
methods are called. If specified, the low watermark must be less
than or equal to the high watermark. Neither high nor low
can be negative.
:meth:~BaseProtocol.pause_writing is called when the buffer size
becomes greater than or equal to the high value. If writing has
been paused, :meth:~BaseProtocol.resume_writing is called when
the buffer size becomes less than or equal to the low value.
The defaults are implementation-specific. If only the
high watermark is given, the low watermark defaults to an
implementation-specific value less than or equal to the
high watermark. Setting high to zero forces low to zero as
well, and causes :meth:~BaseProtocol.pause_writing to be called
whenever the buffer becomes non-empty. Setting low to zero causes
:meth:~BaseProtocol.resume_writing to be called only once the
buffer is empty. Use of zero for either limit is generally
sub-optimal as it reduces opportunities for doing I/O and
computation concurrently.
Use :meth:~WriteTransport.get_write_buffer_limits
to get the limits.
.. method:: WriteTransport.write(data)
Write some data bytes to the transport.
This method does not block; it buffers the data and arranges for it to be sent out asynchronously.
.. method:: WriteTransport.writelines(list_of_data)
Write a list (or any iterable) of data bytes to the transport.
This is functionally equivalent to calling :meth:write on each
element yielded by the iterable, but may be implemented more
efficiently.
.. method:: WriteTransport.write_eof()
Close the write end of the transport after flushing all buffered data. Data may still be received.
This method can raise :exc:NotImplementedError if the transport
(e.g. SSL) doesn't support half-closed connections.
.. method:: DatagramTransport.sendto(data, addr=None)
Send the data bytes to the remote peer given by addr (a
transport-dependent target address). If addr is :const:None,
the data is sent to the target address given on transport
creation.
This method does not block; it buffers the data and arranges for it to be sent out asynchronously.
.. versionchanged:: 3.13 This method can be called with an empty bytes object to send a zero-length datagram. The buffer size calculation used for flow control is also updated to account for the datagram header.
.. method:: DatagramTransport.abort()
Close the transport immediately, without waiting for pending
operations to complete. Buffered data will be lost.
No more data will be received. The protocol's
:meth:protocol.connection_lost() <BaseProtocol.connection_lost>
method will eventually be called with :const:None as its argument.
.. _asyncio-subprocess-transports:
.. method:: SubprocessTransport.get_pid()
Return the subprocess process id as an integer.
.. method:: SubprocessTransport.get_pipe_transport(fd)
Return the transport for the communication pipe corresponding to the integer file descriptor fd:
0: writable streaming transport of the standard input (stdin),
or :const:None if the subprocess was not created with stdin=PIPE1: readable streaming transport of the standard output (stdout),
or :const:None if the subprocess was not created with stdout=PIPE2: readable streaming transport of the standard error (stderr),
or :const:None if the subprocess was not created with stderr=PIPENone.. method:: SubprocessTransport.get_returncode()
Return the subprocess return code as an integer or :const:None
if it hasn't returned, which is similar to the
:attr:subprocess.Popen.returncode attribute.
.. method:: SubprocessTransport.kill()
Kill the subprocess.
On POSIX systems, the function sends SIGKILL to the subprocess.
On Windows, this method is an alias for :meth:terminate.
See also :meth:subprocess.Popen.kill.
.. method:: SubprocessTransport.send_signal(signal)
Send the signal number to the subprocess, as in
:meth:subprocess.Popen.send_signal.
.. method:: SubprocessTransport.terminate()
Stop the subprocess.
On POSIX systems, this method sends :py:const:~signal.SIGTERM to the subprocess.
On Windows, the Windows API function :c:func:!TerminateProcess is called to
stop the subprocess.
See also :meth:subprocess.Popen.terminate.
.. method:: SubprocessTransport.close()
Kill the subprocess by calling the :meth:kill method.
If the subprocess hasn't returned yet, and close transports of stdin, stdout, and stderr pipes.
.. _asyncio-protocol:
Source code: :source:Lib/asyncio/protocols.py
asyncio provides a set of abstract base classes that should be used
to implement network protocols. Those classes are meant to be used
together with :ref:transports <asyncio-transport>.
Subclasses of abstract base protocol classes may implement some or all methods. All these methods are callbacks: they are called by transports on certain events, for example when some data is received. A base protocol method should be called by the corresponding transport.
.. class:: BaseProtocol
Base protocol with methods that all protocols share.
.. class:: Protocol(BaseProtocol)
The base class for implementing streaming protocols (TCP, Unix sockets, etc).
.. class:: BufferedProtocol(BaseProtocol)
A base class for implementing streaming protocols with manual control of the receive buffer.
.. class:: DatagramProtocol(BaseProtocol)
The base class for implementing datagram (UDP) protocols.
.. class:: SubprocessProtocol(BaseProtocol)
The base class for implementing protocols communicating with child processes (unidirectional pipes).
All asyncio protocols can implement Base Protocol callbacks.
.. rubric:: Connection Callbacks
Connection callbacks are called on all protocols, exactly once per a successful connection. All other protocol callbacks can only be called between those two methods.
.. method:: BaseProtocol.connection_made(transport)
Called when a connection is made.
The transport argument is the transport representing the connection. The protocol is responsible for storing the reference to its transport.
.. method:: BaseProtocol.connection_lost(exc)
Called when the connection is lost or closed.
The argument is either an exception object or :const:None.
The latter means a regular EOF is received, or the connection was
aborted or closed by this side of the connection.
.. rubric:: Flow Control Callbacks
Flow control callbacks can be called by transports to pause or resume writing performed by the protocol.
See the documentation of the :meth:~WriteTransport.set_write_buffer_limits
method for more details.
.. method:: BaseProtocol.pause_writing()
Called when the transport's buffer goes over the high watermark.
.. method:: BaseProtocol.resume_writing()
Called when the transport's buffer drains below the low watermark.
If the buffer size equals the high watermark,
:meth:~BaseProtocol.pause_writing is not called: the buffer size must
go strictly over.
Conversely, :meth:~BaseProtocol.resume_writing is called when the
buffer size is equal or lower than the low watermark. These end
conditions are important to ensure that things go as expected when
either mark is zero.
Event methods, such as :meth:loop.create_server,
:meth:loop.create_unix_server, :meth:loop.create_connection,
:meth:loop.create_unix_connection, :meth:loop.connect_accepted_socket,
:meth:loop.connect_read_pipe, and :meth:loop.connect_write_pipe
accept factories that return streaming protocols.
.. method:: Protocol.data_received(data)
Called when some data is received. data is a non-empty bytes object containing the incoming data.
Whether the data is buffered, chunked or reassembled depends on the transport. In general, you shouldn't rely on specific semantics and instead make your parsing generic and flexible. However, data is always received in the correct order.
The method can be called an arbitrary number of times while a connection is open.
However, :meth:protocol.eof_received() <Protocol.eof_received>
is called at most once. Once eof_received() is called,
data_received() is not called anymore.
.. method:: Protocol.eof_received()
Called when the other end signals it won't send any more data
(for example by calling :meth:transport.write_eof() <WriteTransport.write_eof>, if the other end also uses
asyncio).
This method may return a false value (including None), in which case
the transport will close itself. Conversely, if this method returns a
true value, the protocol used determines whether to close the transport.
Since the default implementation returns None, it implicitly closes the
connection.
Some transports, including SSL, don't support half-closed connections, in which case returning true from this method will result in the connection being closed.
State machine:
.. code-block:: none
start -> connection_made
[-> data_received]*
[-> eof_received]?
-> connection_lost -> end
.. versionadded:: 3.7
Buffered Protocols can be used with any event loop method
that supports Streaming Protocols_.
BufferedProtocol implementations allow explicit manual allocation
and control of the receive buffer. Event loops can then use the buffer
provided by the protocol to avoid unnecessary data copies. This
can result in noticeable performance improvement for protocols that
receive big amounts of data. Sophisticated protocol implementations
can significantly reduce the number of buffer allocations.
The following callbacks are called on :class:BufferedProtocol
instances:
.. method:: BufferedProtocol.get_buffer(sizehint)
Called to allocate a new receive buffer.
sizehint is the recommended minimum size for the returned buffer. It is acceptable to return smaller or larger buffers than what sizehint suggests. When set to -1, the buffer size can be arbitrary. It is an error to return a buffer with a zero size.
get_buffer() must return an object implementing the
:ref:buffer protocol <bufferobjects>.
.. method:: BufferedProtocol.buffer_updated(nbytes)
Called when the buffer was updated with the received data.
nbytes is the total number of bytes that were written to the buffer.
.. method:: BufferedProtocol.eof_received()
See the documentation of the :meth:protocol.eof_received() <Protocol.eof_received> method.
:meth:~BufferedProtocol.get_buffer can be called an arbitrary number
of times during a connection. However, :meth:protocol.eof_received() <Protocol.eof_received> is called at most once
and, if called, :meth:~BufferedProtocol.get_buffer and
:meth:~BufferedProtocol.buffer_updated won't be called after it.
State machine:
.. code-block:: none
start -> connection_made
[-> get_buffer
[-> buffer_updated]?
]*
[-> eof_received]?
-> connection_lost -> end
Datagram Protocol instances should be constructed by protocol
factories passed to the :meth:loop.create_datagram_endpoint method.
.. method:: DatagramProtocol.datagram_received(data, addr)
Called when a datagram is received. data is a bytes object containing the incoming data. addr is the address of the peer sending the data; the exact format depends on the transport.
.. method:: DatagramProtocol.error_received(exc)
Called when a previous send or receive operation raises an
:class:OSError. exc is the :class:OSError instance.
This method is called in rare conditions, when the transport (e.g. UDP) detects that a datagram could not be delivered to its recipient. In many conditions though, undeliverable datagrams will be silently dropped.
.. note::
On BSD systems (macOS, FreeBSD, etc.) flow control is not supported for datagram protocols, because there is no reliable way to detect send failures caused by writing too many packets.
The socket always appears 'ready' and excess packets are dropped. An
:class:OSError with errno set to :const:errno.ENOBUFS may
or may not be raised; if it is raised, it will be reported to
:meth:DatagramProtocol.error_received but otherwise ignored.
.. _asyncio-subprocess-protocols:
Subprocess Protocol instances should be constructed by protocol
factories passed to the :meth:loop.subprocess_exec and
:meth:loop.subprocess_shell methods.
.. method:: SubprocessProtocol.pipe_data_received(fd, data)
Called when the child process writes data into its stdout or stderr pipe.
fd is the integer file descriptor of the pipe.
data is a non-empty bytes object containing the received data.
.. method:: SubprocessProtocol.pipe_connection_lost(fd, exc)
Called when one of the pipes communicating with the child process is closed.
fd is the integer file descriptor that was closed.
.. method:: SubprocessProtocol.process_exited()
Called when the child process has exited.
It can be called before :meth:~SubprocessProtocol.pipe_data_received and
:meth:~SubprocessProtocol.pipe_connection_lost methods.
.. _asyncio_example_tcp_echo_server_protocol:
Create a TCP echo server using the :meth:loop.create_server method, send back
received data, and close the connection::
import asyncio
class EchoServerProtocol(asyncio.Protocol):
def connection_made(self, transport):
peername = transport.get_extra_info('peername')
print('Connection from {}'.format(peername))
self.transport = transport
def data_received(self, data):
message = data.decode()
print('Data received: {!r}'.format(message))
print('Send: {!r}'.format(message))
self.transport.write(data)
print('Close the client socket')
self.transport.close()
async def main():
# Get a reference to the event loop as we plan to use
# low-level APIs.
loop = asyncio.get_running_loop()
server = await loop.create_server(
EchoServerProtocol,
'127.0.0.1', 8888)
async with server:
await server.serve_forever()
asyncio.run(main())
.. seealso::
The :ref:TCP echo server using streams <asyncio-tcp-echo-server-streams>
example uses the high-level :func:asyncio.start_server function.
.. _asyncio_example_tcp_echo_client_protocol:
A TCP echo client using the :meth:loop.create_connection method, sends
data, and waits until the connection is closed::
import asyncio
class EchoClientProtocol(asyncio.Protocol):
def __init__(self, message, on_con_lost):
self.message = message
self.on_con_lost = on_con_lost
def connection_made(self, transport):
transport.write(self.message.encode())
print('Data sent: {!r}'.format(self.message))
def data_received(self, data):
print('Data received: {!r}'.format(data.decode()))
def connection_lost(self, exc):
print('The server closed the connection')
self.on_con_lost.set_result(True)
async def main():
# Get a reference to the event loop as we plan to use
# low-level APIs.
loop = asyncio.get_running_loop()
on_con_lost = loop.create_future()
message = 'Hello World!'
transport, protocol = await loop.create_connection(
lambda: EchoClientProtocol(message, on_con_lost),
'127.0.0.1', 8888)
# Wait until the protocol signals that the connection
# is lost and close the transport.
try:
await on_con_lost
finally:
transport.close()
asyncio.run(main())
.. seealso::
The :ref:TCP echo client using streams <asyncio-tcp-echo-client-streams>
example uses the high-level :func:asyncio.open_connection function.
.. _asyncio-udp-echo-server-protocol:
A UDP echo server, using the :meth:loop.create_datagram_endpoint
method, sends back received data::
import asyncio
class EchoServerProtocol:
def connection_made(self, transport):
self.transport = transport
def datagram_received(self, data, addr):
message = data.decode()
print('Received %r from %s' % (message, addr))
print('Send %r to %s' % (message, addr))
self.transport.sendto(data, addr)
async def main():
print("Starting UDP server")
# Get a reference to the event loop as we plan to use
# low-level APIs.
loop = asyncio.get_running_loop()
# One protocol instance will be created to serve all
# client requests.
transport, protocol = await loop.create_datagram_endpoint(
EchoServerProtocol,
local_addr=('127.0.0.1', 9999))
try:
await asyncio.sleep(3600) # Serve for 1 hour.
finally:
transport.close()
asyncio.run(main())
.. _asyncio-udp-echo-client-protocol:
A UDP echo client, using the :meth:loop.create_datagram_endpoint
method, sends data and closes the transport when it receives the answer::
import asyncio
class EchoClientProtocol:
def __init__(self, message, on_con_lost):
self.message = message
self.on_con_lost = on_con_lost
self.transport = None
def connection_made(self, transport):
self.transport = transport
print('Send:', self.message)
self.transport.sendto(self.message.encode())
def datagram_received(self, data, addr):
print("Received:", data.decode())
print("Close the socket")
self.transport.close()
def error_received(self, exc):
print('Error received:', exc)
def connection_lost(self, exc):
print("Connection closed")
self.on_con_lost.set_result(True)
async def main():
# Get a reference to the event loop as we plan to use
# low-level APIs.
loop = asyncio.get_running_loop()
on_con_lost = loop.create_future()
message = "Hello World!"
transport, protocol = await loop.create_datagram_endpoint(
lambda: EchoClientProtocol(message, on_con_lost),
remote_addr=('127.0.0.1', 9999))
try:
await on_con_lost
finally:
transport.close()
asyncio.run(main())
.. _asyncio_example_create_connection:
Wait until a socket receives data using the
:meth:loop.create_connection method with a protocol::
import asyncio
import socket
class MyProtocol(asyncio.Protocol):
def __init__(self, on_con_lost):
self.transport = None
self.on_con_lost = on_con_lost
def connection_made(self, transport):
self.transport = transport
def data_received(self, data):
print("Received:", data.decode())
# We are done: close the transport;
# connection_lost() will be called automatically.
self.transport.close()
def connection_lost(self, exc):
# The socket has been closed
self.on_con_lost.set_result(True)
async def main():
# Get a reference to the event loop as we plan to use
# low-level APIs.
loop = asyncio.get_running_loop()
on_con_lost = loop.create_future()
# Create a pair of connected sockets
rsock, wsock = socket.socketpair()
# Register the socket to wait for data.
transport, protocol = await loop.create_connection(
lambda: MyProtocol(on_con_lost), sock=rsock)
# Simulate the reception of data from the network.
loop.call_soon(wsock.send, 'abc'.encode())
try:
await protocol.on_con_lost
finally:
transport.close()
wsock.close()
asyncio.run(main())
.. seealso::
The :ref:watch a file descriptor for read events <asyncio_example_watch_fd> example uses the low-level
:meth:loop.add_reader method to register an FD.
The :ref:register an open socket to wait for data using streams <asyncio_example_create_connection-streams> example uses high-level streams
created by the :func:open_connection function in a coroutine.
.. _asyncio_example_subprocess_proto:
An example of a subprocess protocol used to get the output of a subprocess and to wait for the subprocess exit.
The subprocess is created by the :meth:loop.subprocess_exec method::
import asyncio
import sys
class DateProtocol(asyncio.SubprocessProtocol):
def __init__(self, exit_future):
self.exit_future = exit_future
self.output = bytearray()
self.pipe_closed = False
self.exited = False
def pipe_connection_lost(self, fd, exc):
self.pipe_closed = True
self.check_for_exit()
def pipe_data_received(self, fd, data):
self.output.extend(data)
def process_exited(self):
self.exited = True
# process_exited() method can be called before
# pipe_connection_lost() method: wait until both methods are
# called.
self.check_for_exit()
def check_for_exit(self):
if self.pipe_closed and self.exited:
self.exit_future.set_result(True)
async def get_date():
# Get a reference to the event loop as we plan to use
# low-level APIs.
loop = asyncio.get_running_loop()
code = 'import datetime as dt; print(dt.datetime.now())'
exit_future = asyncio.Future(loop=loop)
# Create the subprocess controlled by DateProtocol;
# redirect the standard output into a pipe.
transport, protocol = await loop.subprocess_exec(
lambda: DateProtocol(exit_future),
sys.executable, '-c', code,
stdin=None, stderr=None)
# Wait for the subprocess exit using the process_exited()
# method of the protocol.
await exit_future
# Close the stdout pipe.
transport.close()
# Read the output which was collected by the
# pipe_data_received() method of the protocol.
data = bytes(protocol.output)
return data.decode('ascii').rstrip()
date = asyncio.run(get_date())
print(f"Current date: {date}")
See also the :ref:same example <asyncio_example_create_subprocess_exec>
written using high-level APIs.